More than 800 people have been killed and 3,000-3,500 wounded in Syria's besieged eastern Aleppo in the past 26 days, while the remaining trapped civilians await an effective death sentence, the president of the Aleppo local council said on Thursday.

"Today 150,000 people are threatened with extermination. We are calling for a halt to the bombing and guarantees of safe passage of all," Brita Haji Hassan said during a trip to Geneva, where he will meet U.N. Syria envoy Staffan de Mistura on Monday.

Tawfik Chamaa, a representative of the Union of Syrian Medical Relief Organizations (UOSSM), said 1,500 people needed medical evacuation, but any evacuation should have international observers to prevent them being "executed or diverted on the way to hospital".